You said you don't want a part time job, which implies you don't want to invest a lot of your time.
So something like, collecting pop bottles for recycling (I see that all the time, often with either a bike or a shopping cart) might not be for you.

If you have any kind of skill, that other people want, you could make a How To guide.
Quite frequently, popular topics would be How to Make Extra Cash on the Side or How to Find a Guy/Girl.
Your document doesn't need to be long, but it should have the details.
It could be:
How to Run a Pet Walking Business.
How to Run a Lawn Mowing Business.
Whatever, really.

Advertise, which could be a poster on a telephone pole saying send $20 (or $49.99) to wherever... often a higher price is perceived as more legitimate/valuable, than a lower one (experiment for a sweet spot).
If you want to experiment a little, advertise in the classified section of a few papers... or eventually advertise in hundreds of papers.

For each place you advertise, modify your address slightly (you may want to use a PO Box, for privacy).
Station M, <Insert Address>
Department 4132, <Insert Address>
That way, you know which form of advertising is profitable and which is not.